Many articles have surfaces that are coated with one or more protective and/or decorative coatings for any of a variety of reasons. Aerospace vehicles constitute one exemplary category of such articles. Various types of coatings, such as primers and topcoats are commonly applied to various surfaces of aerospace vehicles, such as airplanes or helicopters, as well as many other types of articles. These coatings perform a variety of protective and decorative functions.
In addition, many articles have apertures that may exist, for example, between two components of the article. A sealant is often used to seal such apertures and aerospace vehicles constitute an exemplary category of such articles. Sealants are often used in the manufacture of aircraft for, among other things, integrated fuel tanks and fuel cell cavities. As will be appreciated, such sealants must be resistant to swelling upon prolonged exposure to fuels typically used in such tanks. Other desirable properties for such sealants include high tensile strength, low temperature flexibility, and liquidity at room temperature.
Recently, aircraft manufacturers, in an effort to increase the fuel economy and lifespan of their airplanes, have sought ways to reduce aircraft weight. As a matter of fact, it is believed that even a slight reduction in weight, even as little at 10 pounds, can save hundreds of thousands of dollars over the lifespan of certain aircraft.
As a result, coating and sealant manufacturers have sought to incorporate lightweight fillers into their formulations to reduce the density of certain of their products. A problem, however, has been that only a relatively small amount of such fillers can be added to certain formulations, such as fuel-resistant sealant formulations, without dramatically negatively impacting upon certain properties. One problem associated with these lightweight fillers is that they may exhibit poor chemical resistance to organic solvents, such as fuels to which a composition may be exposed when applied to certain portions of an aircraft. As a result, the incorporation of such lightweight fillers has been limited such that the specific gravity of aerospace sealants, by way of example, has only been successfully reduced from the 1.6 to 1.8 range to a minimum range of approximately 1.0 to 1.2 by virtue of the limited inclusion of such fillers. In addition to fuel resistance, the lightweight fillers can also have a negative impact upon desirable physical properties, such as tensile strength and/or elongation.
Therefore, it would be desirable to provide improved lightweight fillers suitable for use in various compositions, such as coatings and sealants, including, but not limited to, aerospace coating and sealant compositions. In particular, it would be desirable to provide lightweight fillers that can be incorporated into an aerospace sealant composition in an amount sufficient to provide a sealant having a specific gravity of, for example, 0.9 or less, without dramatically negatively impacting upon at least the tensile strength, elongation, and fuel resistance properties of the sealant. The present invention has been developed in view of the foregoing desire.